There have been several recent demonstrations of optical switching systems in which integrated arrays of large numbers (i.e., tens to hundreds) of lithium niobate directional couplers were used for telecommunication applications. For example, in one case, a single package was fabricated containing a total of 48 monolithically integrated 2.times.2 optical waveguide switches connected to form an 8.times.8 rearrangeably non-blocking dilated Benes network. G. D. Bergland, "A Photonic Time Division Switching Experiment," Photonics in Switching Topical Meeting, paper PWB3, Palm Springs, Cal., March, 1993; E. J. Murphy, et al, "Low Crosstalk 8.times.8 Lithium Niobate Switch Array with Uniform Voltages," Optical Fiber Communication Conference, San Jose, Cal., February, 1992; and J. E. Watson, et al., "A Low-Voltage 8.times.8 Ti:LiNbO.sub.3 Switch with a Dilated-Benes Architecture," J. Lightwave Tech., vol. 8, p. 794, (1990).
In another case, twenty-three packages containing a total of 448 2.times.2 optical waveguide switches were interconnected to form a 16.times.16 strictly non-blocking Extended Generalized Shuffle Network. S. S. Bergstein et al., "A Fully Implemented Strictly Non-blocking 16.times.16 Photonic Switching System, Optical Fiber Communication Conference, postdeadline paper, San Jose, Calif., February, 1993 ("the Bergstein article"); A. F. Ambrose, et al., "Design and Performance of a Complete Optical Switching System," Photonics in Switching Topical Meeting, postdeadline paper, Palm Springs, Calif., March, 1993 ("the Ambrose article"); and E. J. Murphy and T. O. Murphy, "Characteristics of Twenty-Three Ti:LiNbO3 Switch Arrays for a Guided Wave Photonic Switching System," European Conference on Integrated Optics, Neuchatel, Switzerland, April, 1993 ("the Murphy article").
In each case, the directional couplers were fabricated using a two-section reverse .DELTA..beta. design. The two-section design uses two sections or pairs of control electrodes covering the waveguides. With this design, each optical switch requires a negative DC bias voltage, V.sub.bias, to obtain the cross state and a positive switch voltage, V.sub.switch, which toggles on and off to obtain the straight-through or bar state. The switches are packaged in a dual-in-line configuration with a bias and switch pin for each coupler. In operation, V.sub.bias is applied to one electrode of each pair while the other electrode of each pair is held at ground to obtain the cross state or switched to V.sub.switch to obtain the bar state. Electronic control boards provide the bias and switching voltages to each of the directional couplers. To maintain low crosstalk levels V.sub.bias and V.sub.switch must be custom tuned for each coupler, because the two-section design is too sensitive to uncontrollable variations in the fabrication process which, without custom tuning, result in significant crosstalk performance degradation. To custom tune V.sub.bias and V.sub.switch expensive, custom voltage drivers with programmable potentiometers are used.
Practical applications involving large switch arrays, however, require optical waveguide switches which can be controlled with easily manufactured and inexpensive, generic voltage drivers and uniform or single preset voltages for V.sub.bias and V.sub.switch. One way to accomplish this, but only for certain system architectures, is to improve the overall system crosstalk performance, as opposed to the crosstalk of the two-section design, by "dilating" the architecture. The problems with this approach include the need for additional couplers for each switch in the array to direct the crosstalk away from the path of the optical signal. The resultant increase in the number of couplers, in turn, increases the complexity of the system design and requires additional and/or larger substrates resulting in a costly design.
Manufacture and operation of optical switching arrays would be greatly simplified if uniform or single preset voltages for the cross and bar states could be applied to every optical switch in an optical network or integrated array and low cross-talk levels maintained without having to "dilate" the architecture.